Preparation of aromatic polyamines



1967 w. DENTON E TAL 3,

PREPARATION OF AROMATIC POLYAMINES Filed April 1, 19 4 C UMP/PE 5 S 0/?I0 INVENTORS WILL /AM 1 DEN TON 12 2/ Z @PH/L/P 0. HAMMOND M A T TO/PNEVUnited States Patent 3,356,729 PREPARATION OF AROMATIQ POLYAMINESWilliam I. Denton, Cheshire, and Philip 1). Hammond, North Haven, Conn,assignors to 01in Mathieson Chemical Corporation, a corporation ofVirginia Filed Apr. 1, 1964, Ser. No. 356,619 12 Claims. (Cl. 260580)ABSTRACT OF TIE DISCLOSURE Aromatic polyamine compounds are prepared bycontinuously adding hydrogen and an aromatic polynitro compound to areaction zone containing powdered palladium while simultaneouslymaintaining the following conditions:

(a) The reaction zone is saturated with hydrogen,

(b) The aromatic polynitro compound is fed to the liquid phase at a rateequivalent to a catalyst loading of no more than about 0.15pound-equivalent of nitro groups per hour per pound of catalyst in thereaction zone,

(c) The concentration of said aromatic polynitro compound in thereaction zone is below about 0.1 percent by weight, and

(d) The liquid phase of the slurry is continuously withdrawn from thereaction zone while retaining the catalyst in the reaction zone.

This invention relates to an improved catalytic hydrogenation ofaromatic polynitro compounds. More particularly, this invention relatesto an improved process for the use of palladium as a catalyst in theliquid phase reduction of aromatic polynitro compounds to the corre-.sponding aromatic polyamine compounds.

Numerous processes have been developed for the catalytic reduction orhydrogenation of aromatic polynitro compounds. However, a number ofproblems have been encountered in attempting to effect the catalytichydrogenation of dinitro or higher polynitro aromatic compounds to thecorresponding aromatic diamines or higher polyamines. In particular, thediand tri-nitro compounds are extremely hazardous at higher tempearturesand can readily cause explosions. For example, trinitrotoluenedecomposes in the range of 130-140 C. Dinitrotoluene is similarlysensitive at a slightly higher temperature. In order to overcome thispotential hazard, it is essential to keep the temperature below thisrange. In the case of the hydrogenation of dinitrotoluene, this can beaccomplished by the use of noble metal catalysts such as platinum orpalladium. The high cost of these catalysts makes it essential tominimize the amount used, or to hydrogenate large quantities of thedinitro compound before the catalyst is poisoned. However, when lowconcentrations of these catalysts are used, long holdup times -20 hours)are necessary.

Nickel catalysts have also been used in both batch and continuousoperations, using high pressures (800-2000 p.s.i.g.) to keep thetemperatures down to a safe level while achieving the desiredconversions.

When fixed bed catalyst systems are employed, there is a rapid decreasein the elfectiveness of the catalyst which is poisoned by the aromaticpolynitro compound reactant and by its reducible contaminants. Inprocesses in which the reaction is carried out by agitating a heatedslurry of catalyst, nitro compound and reaction products, removing theslurry from the reactor and then separating the catalyst by filtrationor other solid-liquid technique and returning it to another reactionbatch, there is also further poisoning of the catalyst after removalfrom the liquid, and a large amount of make-up catalyst must be added.Because of the large consumption of catalyst under these conditions, thecatalyst cost is high.

There is a need in the industry at the present time for an improvedprocess for the preparation of aromatic polyamine compounds frompolynitro compounds.

It is a primary object of the invention to provide an improved processfor the catalytic hydrogenation of arcmatic polynitro compounds.

It is another object of this invention to provide a process forincreasing the effective life of the catalyst employed in thehydrogenation of aromatic polynitro compounds.

Still another object of the invention is to provide an improvedtechnique for separating catalyst from the reaction product obtained bythe hydrogenation of aromatic polynitro compounds.

A further object of the invention is to provide an improved process forreducing dinitrotoluene to toluene diamine in the presence of palladiumcatalyst.

These and other objects of the invention will be apparent from thefollowing detailed description thereof.

A novel continuous process has now been discovered for the catalytichydrogenation of aromatic polynitro compounds in which the foregoingobjects are accomplished. Briefly, in this novel process, the aromaticpolynitro compound is slowly fed to the reaction zone of a reactorcontaining an agitated slurry of catalyst in a solvent for the reactionproduct. Sufficient catalyst is present in the reactor to provide asolids content in the slurry of between about 2 and about 25 percent byweight of the slurry. The aromatic polynitro compound is fed to thereactor at a rate sufiicient to provide a catalyst loading of less thanabout 0.15 pound-equivalent of nitro groups in the arcmatic nitrocompound fed to the reactor per hour per pound of catalyst. During thereaction the catalyst slurry and the reactor contents are maintainedcontinuously saturated with hydrogen. The catalyst slurry, whichcontains the aromatic polyamine reaction product, is continuouslywithdrawn from the reactor through a filter medium in contact with theslurry, thereby permitting removal of the crude liquid reaction productfrom the reactor while retaining the catalyst within the reaction zone.The crude liquid reaction product may be further purified or the crudearomatic polyamine product may be stored for use, as described morefully below.

The term catalyst loading as employed throughout the description andclaims is defined as the pound equivalents of nitro groups in the feedto the reactor per hour per pound of catalyst in the reactor.

The prior art refers to low concentrations of nitro compounds in thereactor, 'but generally a concentration between 2 and 10 percent byweight of the nitro compounds in the reactor is employed. In markedcontrast, in this invention, the concentration of nitro compounds in thereactor is maintained below 0.1 percent and preferably below about 0.015percent by weight. In addition, the prior art employs the term highcatalyst concentration in processes for the reduction of aromatic nitrocompounds, but this term is used generally to define a catalystconcentration up to about 2 percent by weight of the aromatic nitrocompound, which is equivalent to a Weight ratio of about 0.02:1. Inmarked contrast, under the catalyst loading conditions of thisinvention, the weight ratio of catalyst to unreduced nitro compounds inthe reactor is generally of the order of 1200:1 to 1500:1 or higher.Thus it can be seen that, in the process of this invention, a much lowerconcentration of nitro compounds and a much higher concentration ofcatalyst is maintained in the reactor than has been utilized heretofore.As a result of the improved technique of this invention there is amarked increase'in the life of the catalyst, as well as higher product.yields, improved product. purity, and a substantial reduction in thecost of preparing each unit of the aromatic polyamine product. Reducingthe product cost by increasing the catalyst concentration is surprisingand unexpected in view'of the present efforts in the industry to lowercosts by lowering catalyst concentration.

FIGURE 1 is an elevational view of the novel apparatus in which theprocess of this invention can be effected.

FIGURE 2 is a plan view of the novel reactor through the lines 22 ofFIGURE 1.

Referring to FIGURE 1 there is shown a reaction vessel which may beconstructed of steel, stainless steel, or other suitable material ofconstruction capable of withstanding the temperature and pressureconditions employed without rupturing and without being adverselycorroded. At a point adjacent to the bottom of the reaction vessel 10 ahydrogen feed line 11 passes from a hydrogen source under pressure (notshown) through the reaction vessel 10 and is secured to a hydrogen inlet12 positioned to effect maximum distribution of gaseous hydrogenthroughout the reaction vessel 10. It will be recognized by one skilledin the art that the hydrogen may be distributed in any convenient mannerto achieve this distribution.

Aromatic polynitro compound feed line 13 passes through the wall ofreaction vessel 10 at a position near the bottom of the vessel and issecured to aromatic polynitro compound inlet 14. It is preferred thatthe aromatic polynitro compound inlet 14 be positioned to permit feedingof the aromatic polynitro compound at a point approximately in thecenter of reaction vessel 10 in order to obtain substantially uniformcontact with the hydrogen gas escaping from hydrogen inlet 12. However,the aromatic polynitro compound inlet 14 can be positioned at anyconvenient point in reaction vessel 10. Positioned above the aromaticpolynitro compound inlet 14 is a mechanically driven agitator 15 havingat least one set of blades 16 which are connected to agitator shaft 17.Agitator shaft 17 is connected to agitator motor 18, which is powered byelectricity (not shown) or other convenient power supply. If desired,agitation within reaction vessel 10 can be obtained by replacing orsupplementing mechanically driven agitator 15, which is generallypositioned along the central vertical axis of reaction vessel 10, withone or more, and preferably at least four, side entering mechanicallydriven agitators (not shown) spaced equidistant around the periphery ofreaction vessel 10.

A temperature control coil 19 enters the wall of reaction vessel 10 at apoint near the bottom of the vessel, and follows a helical path adjacentto the inner vertical wall of reaction vessel 10, and then passesthrough the wall at a point adjacent to the upper portion of vessel 10.Any suitable temperature control fluid such as water or steam may bepassed through temperature control coil 19 in order to maintain thereaction mass within the desired temperature range. Control of thereaction temperature is obtained by passing fluid of a suitabletemperature to increase or decrease the reaction temperature as desired.To cool the reaction mass, a cooling fluid having a temperaturesubstantially below that of the reaction mass is passed through the coilto lower the temperature of the reaction mass to the desiredtemperature. To heat the reaction mass, a heating fluid having atemperature substantially above the temperature of the reaction mass ispassed through the coil until the temperature is raised to the desiredlevel. While only one coil has been illustrated, it is possible toemploy two or more coils, preferably helically shaped, in order toobtain the desired control of temperature as the reaction progresses.

In addition, external jackets (not shown) may also be employed tocontrol the reaction temperature.

A bafile support ring 20 is positioned with its center along thevertical axis of reaction vessel 10. The ring is preferably positionedbetween the temperature control coil and the central vertical axis ofreaction vessel 10, but any convenient position may be employed. Securedvertically within the baffle support ring are at least two or morevertical baffies 21 positioned substantially equidistant around theinner circumference of baffie support ring 20. If desired, the verticalbafiles 21 may be positioned equidistant around the outer circumferenceof ring 20, or may be attached to the wallof vessel 10. Bafile supportring 20 is secured to the inner wallof reaction vessel 10 by means ofsuitable ring supports 22 or any other convenient securing means.

Positioned along the inner periphery of baffle support ring 20 is atleast one internal filter element 23 and preferably four or moreinternal filter elements positioned vertically. When two or moreinternal filter elements 23 are employed, they are preferably placedequidistant around the inner circumference of bafile support ring 20.Each internal filter element 23 is preferably constructed of sinteredporous stainless steel, having an average pore opening in the range ofbetween about'l and about 20 microns, and preferably between about 2 andabout 5 microns. If desired, internal filter element 23 may beconstructed of stainless steel cloth or screen or any other type ofsuitable cloth or screen having the desired particle size opening. Othertypes of filter media suitable for use as internal filter 23 includeporous plastic or ceramic bayonet filters, and non-woven synthetic fibercovered leaf filter elements. Obviously, the size of the pore opening orscreen opening should be smaller than the particle size of the catalystto retain the catalyst in the reactor. Any convenient solid-liquidseparation technique may be employed in which the catalyst is retainedin the reaction zone while the liquid polyamine reaction product iswithdrawn. Internal filter elements 23 are connected to aromaticpolyamine product discharge line 24, which passes through the wall ofreaction vessel 10 at a position at the top of the vessel. Sufficientpressure drop is maintained across the filter to permit withdrawal ofthe aromatic polyamine product from the reaction vessel 10 throughinternal filter elements 23 into product discharge line 24. Productdischarge line 24 conveys the liquid product to a suitable filtratecollector (not shown). The liquid polyamine reaction product may be thenconveyed to storage or to any suitable processing step.

At a point near the top of reaction vessel 10 is excess hydrogendischarge outlet 25 whichcommunicates with a suitable compressor 26 orother suitable pressure increasing means. Applying pressure in thismanner causes excess hydrogen to pass from the top of reaction vessel 10through excess hydrogen discharge outlet 25 through compressor 26 tohydrogen feed line 11, where excess hydrogen is admixed and recycledwith fresh hydrogen. The resulting mixture is fed to the reactor vessel10 through line 11 to hydrogen inlet 12 and into the reaction mass.

FIGURE 2 is a. plan view of the novel reactor as seen through ahorizontal plane perpendicular to the vertical axis of the reactionvessel 10 through line 22 of FIG- URE 1. FIGURE 2 shows reaction vessel10 having hydrogen feed 11 entering near the bottom of the vertical wallof the vessel to an area below agitator shaft 17 and aromatic polynitrocompound feed line 13, which enters near the bottom of reaction vessel10 and ends underneath agitator 15.

Temperature control coil 19 is a helical coil positioned between thehydrogen inlet 12 and the wall of reaction vessel 10. Battle supportring 20, having vertical baffles 21 secured thereto, is secured by meansof ring supports 22 to the side wall of cylindrical reaction vessel 10.Internal filter elements 23 are positioned vertically and equidistantbetween the baflies 21. Excess hydrogen is fed to hydrogen feed line 11by means of excess hydrogen discharge outlet 25.

The novel process of this invention will be described in more retail ascarried out in the apparatus illustrated in FIGURES 1 and 2. However, itwill be recognized by one skilled in the art that various modificationsin the apparatus may be employed, some of which are described herein,without departing from the invention of the novel process.

At startup, the reactor is charged with a slurry of catalyst particles.The catalyst is preferably finely divided palladium on carbon, but thenovel process of this invention can also be carried out with otherpalladium catalysts such as powdered or pelleted palladium catalystusing kieselguhr, alumina, silica-alumina, etc. as supports. Theparticle size of the catalyst is preferably in the range between about 2and about 200 microns, but larger or smaller size particles can beemployed. As indicated previously, the average particle size of thecatalyst must be larger than the size of the pore openings of the filtermedium employed in order that the catalyst will be retained in thereaction zone.

The liquid component of the slurry catalyst in the reactor at startupmay be any suitable inert solvent for the aromatic polynitro compound.Typical examples of suitable inert solvents for the nitro-substitutedaromatic products include methanol, ethyl acetate, 2-ethoxy-ethanol-l,dimethylformamide, butyl acetate, dibutyl phthalate, glycol ethers suchas ethylene glycol dimethyl ether, mixtures thereof, and the like. Ifdesired, an aromatic polyamine corresponding to the aromatic polynitrocompound reactant may be employed as a solvent, but generally betterresults are obtained when another inert solvent is employed.

The proportion of catalyst should be between about 2 and about 25 andpreferably between about 5 and about percent by weight of the slurry.

Hydrogen is pumped into the slurry under pressure until the desiredpressure is obtained in the reactor and the catalyst slurry is thenheated to a temperature within the operating temperature range.

The catalyst slurry temperature at startup is maintained in a rangebetween about 50 and about 110 C., but after the reaction begins thetemperature may be increased up to about 150 C. It is preferred toemploy a startup temperature between about 85 and about 110 C., and areaction temperature of between about 100 and about 130 C. Highertemperatures may be employed, but higher pressures may also be necessaryin order to prevent volatilization of the solvent or other components ofthe reaction mass.

Sufiicient hydrogen is fed to the reactor through hydrogen inlet 12 toprovide at least the stoichiometric proportion required to reduce thearomatic polynitro compound subsequently fed to the reactor to yield thecorresponding aromatic polyamine compound, and also sufficient hydrogento saturate the reactor contents with hydrogen, including the surfacesof the particles of catalysts, while maintaining a pressure in thereactor in the range between about 50 and about 1000 p.s.i.g., andpreferably in the range between about 100 and about 500 p.s.i.g.Pressures higher than 1000 p.s.i.g. may be employed, if desired. Excesshydrogen in the reactor is continuously withdrawn, as the reactionprogresses, through excess hydrogen discharge outlet 25 at the top ofreactor 10 and is returned by means of blower 26 to the reactor throughhydrogen inlet 12 with make-up hydrogen.

Suflicient agitation is provided by agitator blade 16 in the reactionzone to maintain a substantially uniform suspension of the catalystparticles in the liquid phase in the reactor, and to disperse thehydrogen bubbles throughout the slurry. I

After startup conditions are obtained, as described above, a solution ofthe aromatic polynitro compound reactant is slowly fed to the reactorthrough the aromatic polynitro compound feed line 13 and inlet 14.Typical examples of suitable aromatic polynitro compounds which may bereduced in accordance with the technique of this invention includedinitrotoluene, trinitrotoluene, dinitrobenzene,tetranitrodiphenylethane, nitro-substituted xylenes, hydroxy-substitutedaromatic polynitro compounds such as dinitro cresol, mixtures thereofand the like. The efi'icient catalyst utilization, high product purityand improved yield attained by the process of this invention may also beextended to other nitro compounds, such as nitrobenzene trifluoride,p,p-bis (nitrophenyl)rnethane and the like, but generally the process ofthis invention is more effective when dinitroand trinitro-substitutedaromatic compounds are employed as a reactant.

Since many of the aromatic polynitro compounds are solid at ambienttemperatures, it is preferred to dissolve the aromatic polynitrocompound in a suitable inert solvent of the type described above in aproportion equivalent to between about 10 and about 50, and preferablybetween about 15 and about 35 percent by weight of the resultingsolution prior to feeding it to the reactor. It is possible to melt thearomatic polynitro compound and feed the resulting molten material tothe reactor through aromatic polynitro compound feed line 13. However,because of the close temperature control necessary in order to maintainthe aromatic polynitro compound in a liquid form, it is preferred toemploy a solvent as described more fully below.

The aromatic polynitro compound in solution is fed continuously to thereaction zone through aromatic polynitro compound feed line 13 and inlet14 at a rate equivalent to a catalyst loading of less than about 0.15poundequivalent, and preferably between about 0.01 and about 0.11pound-equivalent of nitro groups per hour per pound of catalyst in thereactor. Because of the relatively low feed rate of the aromaticpolynitro compound to a reactor containing a substantially higherconcentration of catalyst than is normally employed, there issubstantially instantaneous hydrogenation of the aromatic polynitrocompound as it enters the reactor 10. As a result there is usually lessthan 0.005 percent by weight of unreduced nitro compounds in the liquidphase of the reactor at any time, which thereby prevents the rapidpoisoning and deterioration of the catalyst that is normally encounteredin conventional hydrogeneration reactions of this type. In addition,higher yields and improved purity of product at a substantial reductionin cost is obtained. 7

As the reaction progresses, a portion of the liquid phase is withdrawnthrough internal filter element 23 at a rate substantially equal to theliquid feed rate of the aromatic polynitro compound to the reactor. Theliquid phase in reactor 10 predominates in the aromatic polyaminecompound produced by the hydrogenation reaction along with water,solvent, and impurities that may be present in the system. As the liquidphase passes through internal filter element 23, the solid particles ofcatalyst are retained in the reactor by the filter element and aclarified liquid phase is withdrawn from the reactor through aromaticpolyamine compound product discharge line 24.

Agitation of the slurry in the reactor 10 during the reaction must besufiicient to not only maintain a uniform suspension of the catalyst inthe slurry phase, but must also be sufficient to wash away the catalystfilter cake from each internal filter element 23 as it forms, andredisperse it in the slurry phase. The catalyst is generally washed offthe internal filter element 23 by keeping the slurry velocity across theface of internal filter element 23 in excess of twice the liquidvelocity through internal filter element 23.

The clarified liquid phase thus recovered is then distilled to removeany solvent that may be present, and the solvent is recycled fordissolving additional aromatic polynitro compound. The residue ofaromatic polyamine compound and water is then heated to evaporate waterand to remove impurities, which are disposed of by conventional methods.The aromatic polyamine product is then collected and stored for use asdesired.

An important advantage of the novel process of this invention is that noproblems are caused by the water formed during the reaction. In theabsence of aromatic .polynitro compounds, the water is soluble in thesolvent polyamine reaction product, thus eliminating the difficulties ofmulti-phase systems required in prior art techniques.

When the reactor contents are kept saturated with by drogen at all timesand when the feed rate of the aromatic polynitro compound to thereaction zone is maintained within the above mentioned ranges, it ispossible to obtain substantially instantaneous and complete reduction ofthe aromatic polynitro compound to the corresponding aromatic polyaminecompound. As a result of this improved technique, the catalyst life ismarkedly improved, thereby substantially reducing the cost of producingthe aromatic polyamine compound. Failure to maintain the conditionsdescribed above results in premature loss of activity by the catalystand reduced product yields. In addition, when dinitrotoluene ortrinitrotoluene is employed as the aromatic polynitro compound, theexplosion hazard is virtually eliminated, since the concentration ofdinitrotoluene or trinitrotoluene in the reactor at any given time isextremely small.

As the catalyst loading is increased or as the catalyst becomes spent(i.e. begins to lose its reducing activity) side reactions which formundesired resinous products are accelerated. These undesired by-productsreduce the yield and also reduce catalyst life by coating or poisoningthe active centers on the catalyst. However, as described herein, theuse of the proper combination of operating variables to give maximumcatalyst lite also minimizes these undesired side reactions resulting ina product of substantially higher quality and better yields than areobtained using previously known procedures.

One important feature of this invention is that the catalyst must bemaintained in contact with hydrogen at all times when in the presence oftrace quantities of aromatic polynitro compounds in order to prevent itfrom becoming poisoned. In continuous liquid phase reduction processes,maintaining the catalyst in the presence of hydrogen during theseparation is extremely ditficult to accomplish without the loss ofcatalyst life, since the absence of dissolved hydrogen in the liquidphase even for an instant, is sufficient to poison the catalyst in thepresence of aromatic polynitro compounds.

Continuous processes using external filters with catalyst recycle,continuous centrifuges, continuous centrifuges plus magnetic separators,and catalyst settlers to carry out reduction of aromatic nitro compoundshave all been investigated. However, a marked reduction in catalystconsumption, and an increase in product quality and yield have beenobtained using internal filters in the reactor to continuously separatethe product in accordance with the technique of this invention, whilemaintaining the catalyst in an active state in the reactor saturatedwith hydrogen.

The following examples which illustrate the preferred embodiment of thisinvention are presented without any intention of being limited thereby.All parts and percentages are by weight unlessotherwise specified.

Example I An alcohol solution of dinitrotoluene was prepared byagitating molten technical grade dinitrotoluene (approximately 80percent 2,4- and percent 2,6-dinitrotoluene) in methanol at atemperature of about 50 C. Three pounds of methanol were employed foreach Pound of molten dinitrotoluene.

The reactor employed for the reaction was afive gallon autoclaveprovided with internal and external coils to adjust the reactiontemperature as desired. The reactor was also provided with a mechanicalagitator having a speed of 600 revolutions per minute. Secured to theagitator shaft was a four inch diameter turbine typeagitator and a fourinch diameter propeller type agitator, the turbine being positionedabout /3 of a reactor diameter up from the reactor bottom and thepropeller being positioned about one reactor diameter up from thereactor bottom along the shaft. Feed lines for the dinitrotoluene andhydrogen were secured to dip tubes positioned within the autoclave todischarge directly into the eye of the four inch turbine to insureimmediate mixing of both the dimtrotoluene and the hydrogen with thereactor contents. Six porous stainless steel filter elements weresecured within the autoclave to permit separation of the productefiluent from the catalyst particles. The catalyst used was a commercial'5 percent palladium on carbon catalyst.

One pound of 5 percent palladium on carbon catalyst was mixed in threegallons of methanol and the slurry charged to the reactor which was thenpressurized to 400 p.s.i.g. with hydrogen, agitated, and heated to atemperature of 105 C. These temperature, pressure,and agitationconditions were maintained throughout the reaction. The alcohol solutionof dinitrotoluene was then fed to the reactor through a steam tracedline to maintain the solution at about 50 C. in the line. The rate offeed of the alcohol solution of dinitrotoluene was about 22.7 pounds perhour, which was equivalent to a catalyst loading of 0.062pound-equivalent of nitro groups per hour per pound of catalyst, and thesimultaneous feed rate of hydrogen was at the rate of about 0.37 poundper hour. Product was withdrawn from the autoclave at the rate of about23.1 pounds per hour. Equilibrium was quickly attained, and the averageanalysis of the product obtained during the reaction was 16.5 percenttoluene diamine, 0.5 percent residue, 0.004 percent reducibles, 73.2percent methanol, and 9.8 percent water. The reaction continued forabout 330 hours, during which about 14-10 pounds of dinitrotoluene andabout 4230 pounds of methanol were fed to the reactor. During thisentire period the conversion in the reactor never fell below 99.97percent. At the end of this period the catalyst was still as active aswhen initially charged and the run was terminated voluntarily. Acomparison of this example with the results of a similar run(Comparative Test A) employing five times the catalyst loading (the samefeed rate with 0.2 pound catalyst in the reactor) is shown below:

Catalyst Product Quality} Life, lb. weight percent Example CatalystDinitro- Loading toluene] 1b. Reduc- Amine Residue Catalyst: ibles I0.062 1,410 0.03 97.3 2.9 Comparative Test A 0.310 351 0.50 91.1 8. l

The apparatus of Example I was employed and the procedure of Example Iwas followed except that a pressure of 200 p.s.i.g-was used, the feedwas 15 percent dinitrotoluene and percent methanol, and the catalystloading was 0.037 pound-equivalent of nitro groups per hour per pound ofcatalyst (22.6 pounds of dinitrotoluenemethanol solution per hour). Thereaction was carried out for 470 hours during which period 1600 poundsof dinitrotoluene and 9000 pounds of methanol were passed over thecatalyst. During the entire period the. conversion in the reactor neverfell below 99.95 percent. At the end of this period the catalyst wasstill active and the run was terminated voluntarily. A comparison ofthis example with the results of a similar run (Comparative Test B)employing five times the catalyst loading (the same amount of catalystin the reactor with five times the feed rate) is shown below:

1 Pound-equivalents of N per hour per pound of catalyst. 2 After removalof solvent and water. 5 Catalyst still active when run was terminated.

The above example also illustrates that, by modifying the reactionconditions as described in the invention, catalyst life was increasedover 400 percent, yleld increased about 6 percent, and product qualityimproved by reducing the residue 5 percent.

Example III A procedure similar to Example II, employing the ap paratusof Example I, was used in the reduction of tr1- nitrotoluene totriaminotoluene in accordance with the technique of this invention. Asolution of trinitrotoluene in ethyl acetate was prepared by agitatingthe ingredients in the weight ratio of 131 parts of trinitrotoluene to86 9 parts of ethyl acetate at a temperature of 55 C. until asubstantially homogeneous solution was obtained. The reactor was filledwith 2.2 pounds of 0.5 percent palladium on alumina catalyst and threegallons of ethyl acetate. At startup, agitation was started and theresulting slurry of ethyl acetate and catalyst was heated to atemperature of about 100 C. under a hydrogen pressure of about 100p.s.i.g. The agitation, temperature, and pressure con ditions weremaintained throughout the reaction. The ethyl acetate solution oftrinitrotoluene was fed to the reactor by a metering pump through a 60C. warm water jacketed line at a rate of about 42 pounds per hour whichwas equivalent to a catalyst loading of 0.033 pound equivalent of nitrogroups per hour per pound of catalyst. At the same time about 0.5 poundper hour of hydrogen was fed to the reactor and unreacted hydrogen waswith drawn from the top of the reactor. Product efliuent was withdrawnfrom the reactor through the porous stainless steel filter elements atthe rate of about 42.5 pounds per hour. The average analysis of theproduct stream during the 180 hours of operation was about 7.8 percenttoluene tri'amine, about 86.0 percent ethyl acetate and 6.2 per centwater. During thi period 990 pounds of trinitrotoluene and 6560 poundsof ethyl acetate were fed to the reactor. The conversion in the reactornever fell below 99.96 percent during the reaction period.

Example IV Employing the apparatus of Example I, except that a wovenstainless steel screen was employed as the filter medium, the procedureof Example H was modified by introducing 2.0 pounds of 0.5 weightpercent palladium on carbon catalyst, reducing the pressure to 90p.s.i.g. and the temperature to 90 C. These temperature and pressureconditions were maintained throughout the reaction. The rate of feed ofthe alcohol solution of dinitrotoluene was about 16 pounds per hourwhich was equivalent to a catalyst loading of 0.022 pound-equivalent ofnitro groups per hour per pound of catalyst. The reaction continued for750 hours during which time 3000 pounds of dinitrotoluene were fed tothe reactor (equivalent to 1500 pounds of dinitrotoluene per pound ofcatalyst). During this period the conversion never fell below 99.94percent and the stripped toluene diamine product contained 97.0 percentamine equivalents, 3.0 percent residue and only 0.04 percent reducibles.

Example V A 250 cc. stainless steel reactor equipped with agitation,cooling, and an internal porous stainless steel filter was charged with22 grams of 5 percent palladium on carbon catalyst and 220 cc. of aceticacid. It was then pressured to 75 p.s.i.g. with hydrogen with stirringand heated to C. These conditions were maintained throughout the run. A25 percent solution of meta-nitrobenzotrifluoride was made up in aceticacid and fed to the reactor at a rate of 4 cc. per minute. Thisrepresents a catalyst loading of approximately 0.015 pound-equivalent ofnitro groups per hour per pound of catalyst (2.7 poundsnitrobenzotrifluoride per hour per pound of catalyst). After 12 daysoperation the reducibles content (nitrobodies) in the reactor efiiuentwas still 0.006 weight percent or lower and the catalyst showed noreduction in activity.

As indicated above, one unique feature of this invention is the use ofinternal filters in the reactor containing the palladium catalyst in thereaction zone. In a given catalyst system, two factors contribute to thepracticability of the catalyst. One is how long the catalyst can be usedbefore its activity begins to decline and the second is the rate atwhich the catalyst is physically broken down into fine particles whichcannot be recovered and returned to the system.

The foregoing examples have established operating conditions whichmaximize the length of time the catalyst can be used before its activitybegins to fall 01f, resulting in unsatisfactory product. All of thesepreceding examples utilize internal filters in the reactor because othermethods of recovering and recycling the catalyst are not practical inthis system. In all other methods a number of problems prevent achievinga maximum perform ance goal.

First, if the palladium catalyst is removed from the presence ofhydrogen for a very short time while still containing trace amounts ofnitrobodies and catalyst poisons, its activity will immediately decline.Thus, maintaining hydrogen pressure on the catalyst at all times inaccordance with this invention eliminates the excessive catalystpoisoning which occurs in many methods of recovering and recirculatingthe catalyst.

Second, as the catalyst is subjected to agitation, pumping andcirculation, the average particle size is continuously being degraded.As a result catalyst fines are continuously formed. These tines are lostand not returned to the reaction system in many recovery schemes, but inthe novel process of this invention they are retained in the reactor.

The third problem with recovering and reusing the palladium catalyst isthat it does not follow the theoretical physical laws associated withthese materials. For example, settling tests run with fresh catalystshow that it is very simple to settle and effectively separate thepalladium catalyst from solvents such as methanol. However, in actualpractice, the settling rates are not proportional to particle size, norare the rates the same as meas ured in the absence of hydrogen andreaction products. When settling tests were made on reaction productscontaining catalyst, the overflow contained just as high a concentrationof large particles as the settled portion. It was also noted thatsmaller particles appeared in the underflow or settled portion.Experimentation indicated that the low density of the large particleswas due to absorbed hydrogen and hydrogen bubbles sticking to theparticles. As a result, the large particles would not settle out. On theother hand, it was also noted that the smaller particles had a tendencyto stick together, probably as a result of by-product residues acting asa binder. These agglomerates were lighter and also trapped hydrogencaused them to come out with the product. Those agglomerates whichreturned to the reactor were broken up and the fines went out with theproduct in the next pass 1 1 through the separator. The net result wasthat no particle size separations could be obtained by settling orcentrifugal techniques.

Thus it is evident that the use of the internal filter has the followingadvantages which cannot be achieved by any other separation technique.

(1) Catalyst fines formed by a mechanical degradation are containedwithin the reaction zone and continue to contribute to the reductionreaction.

(-2) The catalyst is never starved for hydrogen and, therefore, does notlose activity under the proper operation conditions.

(3) No catalyst is lost due to inefficient separators.

(4) The catalyst starts out "fresh and it is only as the catalystapproaches a spent condition that secondary reactions begin to beobserved and ultimate yield'decreases. At this point, with the internalfilters system the catalyst is immediately replaced maintaining the highultimate yields in contrast to the systems where the catalyst iscontinually approaching the spent state and the average ultimate yieldis lower due to side reactions.

(5) The internal filter avoids the problems of variable settling ratesdue to variable hydrogen absorption on the catalyst encountered in manyof the other separation systems.

Various modifications of the invention, some of which have been referredto above, may be employed, without departing from the spirit of thisinvention.

What is desired to be secured by Letters Patent is:

1. In the continuous process for the catalytic hydrogenation of anaromatic polynitro compound in the liquid phase in the presence of apalladium catalyst to yield the corresponding aromatic polyamine,wherein said aromatic polynitro compound and hydrogen are continuouslyfed to a reaction zone containing an agitated slurry of palladiumcatalyst, the improvement which comprises simultaneously andcontinuously (a) maintaining the reaction zone saturated with hy- (b)feeding said aromatic polynitro compound free of.

catalyst to the liquid phase at a rate equivalent to a catalyst loadingof no more than about 0.15 poundequivalent of nitro groups per hour perpound of catalyst in the reaction zone,

(c) maintaining the concentration of said aromatic polynitro compound inthe reaction zone below about 0.1 percent by weight,

(d) continuously withdrawing from the reaction zone a portion of theliquid phase of said slurry while retaining said catalyst in thereaction zone, and

(e) maintaining the catalyst concentration within the reaction zonebetween about 2 and 25 percent by weight of said slurry.

'2. The process of claim 1 wherein said aromatic poly nitro compound isadded to the reaction zone at a rate equivalent to between about 0. 01and about 0.11 poundequivalent of nitro groups per hour per pound ofcatalyst in the reaction zone.

3. The processot claim 1 wherein said aromatic polynitro compound is fedto said reaction zone dissolved in an inert solvent for said aromaticpolynit'ro compound.

4. The process of claim 3 wherein said inert solvent is methanol.

5. The process of claim 3 wherein said inert solvent is ethyl acetate.

6. The process of claim 1 wherein said aromatic polynitro compound isdinitrotoluene.

7. The process of claim 1 wherein said aromatic polynitro compound istrinitrotoluene.

8. The process of claim 3 wherein said aromatic polynitro compound isdinitrotoluene and said inert solvent is methanol.

9. In the continuous process for the catalytic hydrogenation of anaromatic polynitro compound in the liquid phase in the presence of apalladium catalyst to yield the corresponding aromatic polyamine,wherein hydrogen and a solution of an aromatic polynitro compound in aninert solvent therefor are continuously fedto a reaction zone containingan agitated catalyst slurry, the improvement which comprisessimultaneously and. continuously (a) maintaining the reaction zonesaturated with hydrogen,

(b) maintaining the reaction zone under a pressure of between about andabout 1000 p.s.i.g.,

(c) maintaining the temperature of the reaction zone within the rangebetween about 50 and about 150 C.,

(d) feeding said aromatic vpolynitro compound free of catalyst to thereaction zone at a rate equivalent to a catalyst loading of 'no morethan about 0.15 pound-equivalent "of nitro groups per "hour per pound ofcatalyst,

(e) maintaining the concentration of said aromatic polynitro compound inthe reaction zone below about 0.1 percent by weight,

( f) continuously withdrawing from the reaction zone a portion of theliquid phase of said slurry while retaining said catalyst in the reactorzone, and

(-h) maintaining the catalyst concentration within the reaction zonebetween about 2 and about 25 percent by weight of said slurry.

10. The process of claim 9 wherein said inert solvent is methanol.

11. The process of claim 10 wherein said aromatic polynitro compound isdinitr'otoluen'e.

12. The process of claim '10 wherein said aromatic polynitro compound istrinitrotoluene.

References Cited UNlTED STATES PATENTS 2388,608 11/1945 Emerson 260--85O2,619,503 11/1952 'Be'nner et al. 260-850 2,894,036 7/ 1959 Graham 260 53,154,584 10/1964 Gardner :26 058O 3,232,989 2/1966 Graham 260-580CHARLES B. PARKER, Primary Examiner.

N. A. WICZER, P. C. IVES, Assistant Examiners.

1. IN THE CONTINUOUS PROCESS FOR THE CATALYTIC HYDROGENATION OF ANAROMATIC POLYNITRO COMPOUND IN THE LIQUID PHASE IN THE PRESENCE OF APALLADIUM CATALYST TO YIELD THE CORRESPONDING AROMATIC POLYAMINE,WHEREIN SAID AROMATIC POLYNITRO COMPOUND AND HYDROGEN ARE CONTINUOUSLYFED TO A REACTION ZONE CONTAINING AN AGITATED SLURRY OF PALLADIUMCATALYST, THE IMPROVEMENT WHICH COMPRISES SIMULTANEOUSLY ANDCONTINUOUSLY (A) MAINTAINING THE REACTION ZONE SATURATED WITH HYGEN, (B)FEEDING SAID AROMATIC POLYNITRO COMPOUND FREE OF CATALYST TO THE LIQUIDPHASE AT A RATE EQUIVALENT TO A CATALYST LOADING OF NO MORE THAN ABOUT0.15 POUNDEQUIVALENT OF NITRO GROUPS PER HOUR PER POUND OF CATALYST INTHE REACTION ZONE, (C) MAINTAINING THE CONCENTRATION OF SAID AROMATICPOLYNITRO COMPOUND IN THE REACTION ZONE BELOW ABOUT 0.1 PERCENT BYWEIGHT, (D) CONTINUOUSLY WITHDRAWING FROM THE REACTION ZONE A PORTION OFTHE LIQUID PHASE OF SAID SLURRY WHILE RETAINING SAID CATALYST IN THEREACTION ZONE, AND (E) MAINTAINING THE CATALYST CONCENTRATION WITHIN THEREACTION ZONE BETWEEN ABOUT 2 AND 25 PERCENT BY WEIGHT OF SAID SLURRY.